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Microsoft Word 4 Dominguez Castells 10pix 1line final Journal of Human Kinetics volume 32/2012, 33 41 DOI 10 2478/v10078 012 0021 9 33 Section Swimming 1 Department of Physical Education and Sport, Fa[.]

Effect of Different Loads on Stroke and Coordination Parameters

During Freestyle Semi-Tethered Swimming

by

The aim of this study was to analyse to what extent the use of different loads modifies freestyle stroke and coordination parameters during semi-tethered swimming, and to examine whether those changes are positive or negative to swimming performance First, behaviour of swimming speed (v), stroke rate (SR) and stroke length (SL) with increasing loads was examined Secondly, mean and peak speed of propulsive phases (propv mean and propv peak ) were analysed, as well as the relative difference between them (%v) Finally, index of coordination (IdC) was assessed Eighteen male swimmers (22.10±4.31years, 1.79±0.07m, 76.74±9.00kg) performed 12.5m maximal sprints, pulling a different load each trial (0, 1.59, 2.21, 2.84, 3.46, 4.09, 4.71, 5.34, 5.96, 6.59, 7.21 and 7.84kg) Rest between repetitions was five minutes Their feet were tied together, keeping a pull-buoy between legs and isolating the upper limb action A speedometer was used to measure intra-cycle speed and the test was recorded by a frontal and a lateral underwater cameras Variables v and SL decreased significantly when load increased, while SR remained constant (p<0.05) Propv mean and propv peak decreased significantly with increasing loads (p<0.05) In contrast, %v grew when load rose (r = 0.922, p<0.01), being significantly different from free swimming above 4.71kg For higher loads, swimmers did not manage to keep a constant velocity during a complete trial IdC was found to increase with loads, significantly from 2.84kg (p<0.05) It was concluded that semi-tethered swimming is one training method useful to enhance swimmers’ performance, but load needs to be individually determined and carefully controlled

Key words: intra-cycle speed, propulsive phases, index of coordination, resisted training

Introduction

In swimming, race time can be divided into

four components: start time, swimming time, turn

time and finish time (Arellano et al., 1994)

Regarding actual swimming, the time needed to

complete one lap can be considered as a function

of stroke rate and stroke length As in other

cyclical activities, swimmers need to find the

optimal compromise between stroke rate and

stroke length to attain and keep the maximal

velocity during a race (Alberty et al., 2005)

Numerous studies have been carried out to

observe and understand the evolution of this “SL

× SR” model during competitive events (Arellano

et al., 1994; Chollet et al., 1997; Craig et al., 1985)

Throughout the race, as fatigue develops, speed and stroke length decrease whereas stroke rate remains constant or slightly increases at the end

of the race (Alberty et al., 2009; Chollet et al., 1997; Craig et al., 1985; Hay, 2002; Keskinen and Komi, 1993) Swimmers can choose different strategies to develop their maximal speed as a function of the race distance and they attempt to maintain this chosen speed in spite of fatigue throughout the race

Stroke rate and stroke length combinations (and, therefore, speed values) are determined by several factors such as anthropomorphic variables, muscle strength, physical conditioning

and swimming economy (Pelayo et al., 2007)

Another factor with big influence on swimming

speed is load (Shionoya et al., 1999) In the latter

study, they assessed speeds from 1.34m/s with

1kg load to 0.45m/s with 10kg load, but stroking

parameters were not studied To our knowledge,

only one recent study has analysed speed, stroke

rate and stroke length while semi-tethered

swimming with increasing resistances

(Gourgoulis et al., 2010)

In contrast, swimming speed during

propulsive stroke phases has not been previously

studied under resisted conditions Considering

the stroke phases proposed by Chollet et al.,

(2000), we can distinguish two propulsive phases

(pull and push) and two non-propulsive ones

(entry-catch and recovery) Regardless of every

individual combination of stroke rate and stroke

length, swimming speed is expected to be higher

during propulsive phases in both free and

semi-tethered swimming Intra-cycle velocity variations

were studied at different swimming paces

(Schnitzler et al., 2010) and while swimming with

parachute (Schnitzler et al., 2011), but not with

different loads To the authors’ knowledge, only

one study (Telles et al., 2011) has examined

changes in index of coordination (IdC) in three

different resisted swimming conditions

Therefore, the aim of the present study was

to analyse to what extent the use of different loads

modifies freestyle stroke and coordination

parameters during semi-tethered swimming, and

to examine whether those changes are positive or

negative to swimming performance With this

analysis it was intended to bring light to the value

of semi-tethered swimming for training purposes

Materials and Methods

Participants

A group of 18 male college swimmers

volunteered to participate in our study (mean age

22.10±4.31years, stature 1.79±0.07m, arm span

1.85±0.08m and body mass 76.74±9.00kg) All of

them had trained in swimming for at least 5 years

and had competed at regional or national level

(25m time, in-water start =14.84±1.21s) The

protocol was fully explained to them before they

provided written consent to participate in the

study, which was approved by the university

ethics committee

Procedures

The test was conducted in one swimming pool session, at the end of the competitive season

It consisted in 12.5m swimming across the pool, at maximal speed, pulling a different load each trial, which was added by means of a pulley system The swimmers rested five minutes between two consecutive repetitions After a standardized 800m warm-up, first load was 4.5kg and it increased 2.5kg each trial Considering the pulley system effects (mechanical advantage, friction and components weight), real loads pulled by the swimmers were 0, 1.59, 2.21, 2.84, 3.46, 4.09, 4.71, 5.34, 5.96, 6.59, 7.21 and 7.84kg This was checked prior to the test, in the same conditions Swimmers were connected to the load by means

of a rope and a belt Their feet were tied together, keeping a pull-buoy between legs and isolating the upper limb action They were asked not to breathe during each trial to keep head position constant

Measurements

A speedometer attached to the swimmer’s belt was used to measure intra-cycle swimming speed (Sportmetrics S.L., Spain, frequency: 200

Hz, accuracy: 0.1mm) The test was recorded by a frontal and a lateral underwater cameras (Sony, frequency: 50 Hz, shutter speed: 1/250s), fixed to the pool wall

Analysis

Intra-cycle speed was recorded for every participant and trial It was sampled at a frequency of 200 Hz and subsequently smoothed with a low-pass Butterworth filter with a cut-off frequency of 5 Hz For each trial, three middle strokes were selected to avoid both the effect of the impulse from the wall and the speed decrease

at the end One stroke started when one hand first touched the water while entering it and finished the next time the same event happened for the same hand Mean speed (v) was calculated for these 3 strokes Stroke rate (SR) was calculated from the 3 strokes time:

SR (Hz) = number of strokes / strokes time (s)

Then, stroke length (SL) was obtained with the following equation:

( / )

v m s

SL m cic

SR Hz

 Average of every variable for the whole group and every single load was calculated and represented Intra-cycle speed curves were

compared among swimmers and loads, to try to

find any repeated patterns

Within the stroke phases defined by

Chollet et al (2000), ‘pull’ and ‘push’ were

considered the propulsive ones ‘Pull’ phase starts

after the hand´s entry into the water, when it

reaches the most forward point and begins to

move backwards It ends when the hand is under

the shoulder, on an imaginary vertical line Here

begins the ‘push’ phase, which ends at the

moment the hand is completely out of water

With intra-cycle speed and video images mean

and peak speed for the propulsive phases (pull

and push) in three strokes (propvmean and

propvpeak, respectively) were obtained for each

trial and swimmer In addition, percentage of

increase from propvmean to propvpeak (%v) was

calculated This variable was used as an indicator

of propulsive intra-cycle velocity fluctuations

magnitude Video analysis allowed us to calculate

index of coordination (IdC) for every trial As for

the stroke parameters, average IdC, propvmean,

propvpeak and %v for the group and every load

were calculated and represented

Statistical analysis

Descriptive statistics was used to calculate

means and standard deviations All variables (v,

SR, SL, propvmean, propvpeak, %v and IdC) were

tested for normality (Shapiro-Wilk test) After

performing Levene’s test for variance

homogeneity, one-way repeated measures

ANOVA was used to assess differences among

loads for every variable A two-way ANOVA was

used to compare propvmean and propvpeak along

the test Finally, Pearson’s correlation coefficients

were calculated between load and the rest of

variables The statistical analysis was carried out

using a statistical software package (SPSS 15.0)

Statistical significance was set at p<0.05

Results

Behavior of v, SR and SL during semi-tethered swimming with increasing loads is represented in Figure 1 Stroke rate did not change significantly when load did (0.97±0.02Hz)

In contrast, v and SL decreased with increasing loads (r = -0.985, -0.989, respectively, p<0.01) (Table 1) Range of values was: v: 1.41-0.16m/s; SL: 1.52-0.17m/cic

When comparing intra-cycle speed curves among participants and loads three main patterns were observed (Figure 2) Regardless of the impulse from the wall, speed followed a horizontal trend for the first six loads (until 4.71kg) (Fig 2a) For the next two loads (5.34-5.96kg) speed decreased progressively in the first part of the trial and then remained constant in the second part (Fig 2b) Finally, for the highest loads (6.59kg and higher) speed described a concave upward curve, dropping quickly at the beginning and more gradually at the end, until reaching 0m/s (Fig 2c)

Variable propvpeak was significantly higher than propvmean (p<0.05) and they were positively correlated (r = 0.995, p<0.01) Mean speed in propulsive stroke phases (propvmean) decreased significantly with increasing loads in semi-tethered swimming (r = -0.984, p<0.01) (Table 1), from 1.39±0.17m/s with 0kg to 0.25±0.10m/s with 7.84kg load (Figure 3) Peak speed (propvpeak) dropped significantly from 1.79±0.17m/s with 0kg

to 0.73±0.22m/s with 5.96kg load (first nine loads) and did not change significantly for the highest loads (r = -0.971, p<0.01)

Table 1

Pearson´s correlation coefficients between load and the rest of variables

*: p<0.01; ns : not significant propv mean : mean speed of propulsive stroke phases (pull+push);

propv peak : peak speed of propulsive stroke phases;

%v: percentage of increase from propv mean to propv peak

(m/cic)

propv mean

(m/s)

propv peak

(m/s)

%v IdC

(%)

c b

v: y = -0,1744x + 1,4228

R² = 0,98

SL: y = -0,1818x + 1,4829

R² = 0,98

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8

load (kg)

v (m/s)

SR (Hz)

SL (m/cic)

Figure 1

Behavior of some stroking parameters during semi-tethered swimming

Error bars are standard deviation (SD)

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12 14

v

(m

/s

)

time (s)

0 0.5 1 1.5 2 2.5 3

0 2 4 6 8 10 12 14 16

v (m /s )

time (s)

0 0.5 1 1.5 2 2.5 3

0 2 4 6 8 10 12

v (m /s )

time (s)

Figure 2

Behavior patterns of intra-cycle speed while semi-tethered swimming

a) 4.09kg load; b) 5.96kg load; c) 7.84kg load

The analysis started from the dotted line

a

Figure 3

Mean and peak speed of propulsive phases (pull+push) while semi-tethered swimming

Error bars are standard deviation (SD)

y = 3,85x 2 - 9,7619x + 31,482

R² = 0,99

0 50 100 150 200 250 300

% v

load (kg)

Figure 4

Percentage of increase from mean to peak propulsive speed during semi-tethered swimming

Error bars are standard deviation (SD)

y = 1,0633x + 6,7734 R² = 0,88

4 6 8 10 12 14 16 18 20

IdC (%)

load (kg)

Figure 5

Index of coordination during semi-tethered swimming

Error bars are standard deviation (SD)

Percentage of increase from mean to peak

speed in the propulsive phases (%v) did not

undergo any significant changes neither from 0kg

to 4.09kg load (first six trials; %v = 36.94±9.57%)

nor from 6.59kg to 7.21kg load (%v =

149.23±13.21%) (Figure 4) In contrast, it increased

significantly and in a quadratic way when load

raised between 4.09kg and 6.59kg and from

7.21kg to 7.84kg, when it almost reached 200% (r =

0.922, p<0.01) Consistently, propvmean and

propvpeak were negatively correlated with %v (r =

-0.871, -0.824, respectively, p<0.01)

Coordination mode used in free and

semi-tethered swimming was superposition (IdC>0%)

IdC was 6.6±4.6% when swimming free and it

increased significantly with loads (p<0.05), from

7.1±5.3% with 1.59kg to 14.8±3.7% with 7.84kg

(Figure 5) High positive significant correlation

was found between load and IdC (r = 0.910,

p<0.01)

Discussion

The aim of the present study was to analyse

the effect of different loads on freestyle stroke and coordination parameters during semi-tethered swimming and to examine whether those changes are positive or negative to swimming performance The main findings of our study showed that percentage of increase from mean to peak speed in the propulsive phases grew following a quadratic trend with increasing loads Besides, IdC rose significantly with load Three different intra-cycle velocity patterns were noticed throughout loads

Swaine and Reilly (1983) stated that freely chosen stroke rate led to maximum swimming speed Strictly, combination of stroke rate and stroke length determines swimming speed (v = SR·SL) For that reason, most swimmers try to increase SR when SL starts to decrease due to fatigue (Alberty et al., 2009; Craig et al., 1985; Keskinen and Komi, 1993; Pelayo et al., 2007) If they do not achieve it, their swimming speed decreases (Alberty et al., 2005) In the present study, rest between consecutive trials was five minutes, so fatigue did not appear As expected, v and SL dropped when load increased, due to the

increased drag Significant drop compared to free

swimming was observed in these variables from

the first load On the other hand, SR did not

change significantly when speed (and load) did

This was consistent with the studies conducted by

Alberty et al (2005) and Pelayo et al., (1996)

Gourgoulis et al (2010) reported that SR dropped

when swimming with loads compared to free

swimming, but no difference was found in SR

between loads However, in some other studies

(Alberty et al., 2009; Craig et al., 1985; Keskinen

and Komi, 1993; Pelayo et al., 2007) swimmers

managed to increase SR when speed started to

decrease This difference is presumably owing to

the fact that the limiting factor in our case was not

fatigue, but load There was not a point where v,

SL or SR trends clearly changed (Fig 1), but it is

interesting to observe that they all intersected

close to 1m/s, around 2.84kg load

To the best of our knowledge, there are no

studies which have compared intra-cycle speed

while semi-tethered swimming, pulling different

loads We observed three main patterns (Fig 2)

Only for the first loads, up to 4.71kg, swimmers

were able to keep a constant and relatively high

average speed (0.9m/s) after a sharp decrease due

to the impulse from the wall In the rest of trials,

excessive load made average 3 strokes speed drop

to 0.5-0m/s Speed reduction was linear and

longer in time until swimmers reached a stable

speed for next two loads In the last trials, load

was too high for the swimmers to keep any

constant speed, so it decreased gradually during

the whole trial until 0m/s

To the authors’ knowledge, no previous

investigation has analysed speed during

propulsive phases while semi-tethered

swimming Shionoya et al (1999) assessed

average speed during semi-tethered swimming

with several loads: 1, 4, 7 and 10kg The values

obtained were: 1.34, 1.07, 0.79 and 0.45m/s, which

are similar to our propvpeak data, considering that

loads were slightly different In the present study,

peak speed was significantly higher than mean

speed during propulsive phases in semi-tethered

swimming (p<0.05) Like in stroke parameters,

significant decrease compared to zero load was

observed in propvmean and propvpeak from the first

resisted condition In contrast, no significant

change in peak propulsive speed was observed

over 5.96kg, but this was not enough to enable

swimmers to reach a stable speed during a trial This stagnation of propvpeak may be owing to the fact that, despite having their legs tied, most swimmers tried to move them for stabilization when swimming with the highest loads, what turned into a bigger propulsion and higher speed Despite this, there was a high correlation between load and peak speed (r = -0.971, p<0.01) On the other hand, significant change in %v compared to

no load condition was first noticed with 4.71kg This was also the last load with which swimmers could keep a constant speed during the whole trial As a whole, the higher the load, the lower the mean and peak speed of propulsive phases and the bigger the relative difference between them (%v) This means that intra-cycle speed variations became larger with higher loads This may have happened because the swimmers may have tried to jerk to move forward pulling too heavy loads

Skilled swimmers increased IdC when speed increased while swimming free (Schnitzler,

et al., 2010; Schnitzler, et al., 2008) or when speed decreased while swimming with added resistance (parachute, paddles or both) (Schnitzler et al., 2011; Telles et al., 2011) In agreement with this, in the present study IdC increased with growing load and decreasing velocity Significant change compared to free swimming first happened with 2.84kg This change in coordination is probably the consequence of the swimmers’ adaptations to higher drag minimizing energy costs They enhanced relative duration of propulsive phases (pull+push) (Gourgoulis et al., 2010) and overlapped propulsive forces of both arms to overcome increased drag (Maglischo et al., 1984) Semi-resisted training may be, therefore, useful to change coordination mode to superposition or to consolidate it, which has been proved to be the more widely used by expert swimmers (Seifert et al., 2004)

Resisted training in swimming enhanced swimming speed (Girold et al., 2006; Mavridis et al., 2006) and strength (Girold et al., 2006; Girold

et al., 2007) Conversely, after comparing tethered and non-tethered stroke mechanics, it was concluded that repeated tethered training would entail detrimental adjustments in swimming technique and, therefore, swimmers’ performance would probably deteriorate (Maglischo et al., 1984) Nevertheless, no negative changes would

be expected if tethered swimming was only a part

of the training program (Maglischo et al., 1985)

According to Shionoya et al (1999), the most

suitable load for training is the load which

produces the maximum power in the force-power

curve Further research is required to determine

whether a relationship between swim power

production and stroke and coordination

parameters exists

Summing up, the most interesting findings

of this study were that, over 4.71kg load, a

constant swimming speed could not be

maintained during a short period of time, and

differences between mean and peak propulsive

speed were significantly higher than in free

swimming Besides, IdC was found to increase

with loads, significantly over 2.84kg In light of

the results, it is suggested that optimal load for resisted training in swimming should be individually determined between 2.84 and 4.71kg (swimming speed between 0.91 and 0.54m/s, respectively)

As a concluding remark, it can be stated that semi-tethered swimming is one training method to enhance swimmers’ performance, although load needs to be carefully controlled Our results showed that stroke and coordination parameters were not modified to a great extent under certain load Moreover, resisted training would be beneficial to coordination mode Training load should be, however, individually determined

Acknowledgements

The authors would like to thank the swimmers for their kind cooperation This study was possible thanks to an FPU fellowship AP2008-03243

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Corresponding author:

Rocio Dominguez Castells

Department of Physical Education and Sport

Faculty of Sport Sciences

University of Granada, Spain, Ctra Alfacar, s/n, 18011, Granada (Spain)

Phone: (+34) 645191078

E-mail: rdc@ugr.es